A platinum coating having high brightness has been conventionally formed on the outermost layer of an abrasion-resistant layer for improving the scratch resistance of exterior parts, ornaments such as glasses, accessories, and watches, decorative trims, sporting goods, and the like in order to make a high-grade appearance. For example, in Patent Literature 1, an undercoat layer is formed on a base, a titanium carbide layer is formed on the surface thereof by a dry plating method, and a decorative coating layer comprising platinum or a platinum alloy formed by a dry plating method is formed on the surface thereof. However, it has been necessary to thinly form the film since the platinum layer as the outermost layer has been expensive; and it has been necessary to make the titanium carbide layer to have a pale color in order to suppress color change due to peeling of the thin platinum layer. Therefore, the hardness of the titanium carbide layer has been low (about 40%) compared to the hardness of a typical titanium carbide layer, and it has been impossible to obtain sufficient scratch resistance.
Further, when hardness is increased by increasing the amount of carbon allowed to react with the titanium carbide layer in order to improve scratch resistance, a color tone is darkened although the scratch resistance is improved. Further, there is a problem that peeling of a film due to increasing film stress and pitting corrosion in a corrosion resistance test are prone to occur when the film thickness of the titanium carbide layer which is a hardened layer is increased in order to similarly improve scratch resistance. Thus, it has been difficult to form the film having a film thickness of 1.0 μm or more.
Furthermore, there has been a problem that a platinum-based coating causes an allergy by bringing the coating into contact with the human skin.